Link thumbnails: post og:image previews + WOTD default-off

URL link previews now post the page's og:image as an inline m.image
thumbnail above the title/description reply. All outbound fetches in the
preview path (page scrape, image HEAD probe, image download) route through
a new SSRF/DoS-hardened safehttp client so a posted link can't steer
fetches at loopback/RFC1918/cloud-metadata IPs or OOM the parser.

Also flips the daily WOTD auto-post to opt-in (ENABLE_WOTD_POST=true)
instead of opt-out.
This commit is contained in:
prosolis
2026-06-24 21:55:25 -07:00
parent cbfca525f5
commit 8122973b74
7 changed files with 443 additions and 37 deletions

View File

@@ -7,6 +7,11 @@ BOT_DISPLAY_NAME=GogoBee
# Which rooms the bot posts scheduled content to (comma-separated room IDs) # Which rooms the bot posts scheduled content to (comma-separated room IDs)
BROADCAST_ROOMS=!roomid:example.com BROADCAST_ROOMS=!roomid:example.com
# The daily 08:00 WOTD auto-post is disabled by default.
# Set to true to enable it. The !wotd command and passive WOTD
# usage tracking work regardless of this setting.
ENABLE_WOTD_POST=false
# Admins who can run admin-only commands (comma-separated Matrix user IDs) # Admins who can run admin-only commands (comma-separated Matrix user IDs)
ADMIN_USERS=@yourmxid:example.com ADMIN_USERS=@yourmxid:example.com

View File

@@ -333,6 +333,9 @@ func runMigrations(d *sql.DB) error {
// engages when a fork / elite / boss / supply pinch actually // engages when a fork / elite / boss / supply pinch actually
// needs a decision. CAS-claim on this column gates re-entry. // needs a decision. CAS-claim on this column gates re-entry.
`ALTER TABLE dnd_expedition ADD COLUMN last_autorun_at DATETIME`, `ALTER TABLE dnd_expedition ADD COLUMN last_autorun_at DATETIME`,
// URL link previews now post the page's og:image/twitter:image
// thumbnail; cache it alongside the title/description.
`ALTER TABLE url_cache ADD COLUMN image_url TEXT NOT NULL DEFAULT ''`,
} }
for _, stmt := range columnMigrations { for _, stmt := range columnMigrations {
if _, err := d.Exec(stmt); err != nil { if _, err := d.Exec(stmt); err != nil {
@@ -1124,6 +1127,7 @@ CREATE TABLE IF NOT EXISTS url_cache (
url TEXT PRIMARY KEY, url TEXT PRIMARY KEY,
title TEXT DEFAULT '', title TEXT DEFAULT '',
description TEXT DEFAULT '', description TEXT DEFAULT '',
image_url TEXT NOT NULL DEFAULT '',
cached_at INTEGER DEFAULT (unixepoch()) cached_at INTEGER DEFAULT (unixepoch())
); );
@@ -2041,15 +2045,15 @@ func SeedSchedulerDefaults(d *sql.DB) error {
name string name string
cron string cron string
}{ }{
{"prefetch", "5 0 * * *"}, // 00:05 daily {"prefetch", "5 0 * * *"}, // 00:05 daily
{"maintenance", "0 3 * * *"}, // 03:00 daily {"maintenance", "0 3 * * *"}, // 03:00 daily
{"wotd", "0 8 * * *"}, // 08:00 daily {"wotd", "0 8 * * *"}, // 08:00 daily
{"holidays", "0 7 * * *"}, // 07:00 daily {"holidays", "0 7 * * *"}, // 07:00 daily
{"releases", "0 9 * * 1"}, // 09:00 Monday {"releases", "0 9 * * 1"}, // 09:00 Monday
{"birthday_check", "0 6 * * *"}, // 06:00 daily {"birthday_check", "0 6 * * *"}, // 06:00 daily
{"anime_releases", "0 10 * * *"},// 10:00 daily {"anime_releases", "0 10 * * *"}, // 10:00 daily
{"movie_releases", "0 11 * * *"},// 11:00 daily {"movie_releases", "0 11 * * *"}, // 11:00 daily
{"concert_digest", "0 12 * * 0"},// 12:00 Sunday {"concert_digest", "0 12 * * 0"}, // 12:00 Sunday
} }
stmt, err := d.Prepare(`INSERT OR IGNORE INTO scheduler_config (job_name, cron_expr) VALUES (?, ?)`) stmt, err := d.Prepare(`INSERT OR IGNORE INTO scheduler_config (job_name, cron_expr) VALUES (?, ?)`)

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@@ -0,0 +1,184 @@
package plugin
import (
"bytes"
"context"
"fmt"
"image"
_ "image/gif" // register GIF decoder for DecodeConfig
_ "image/jpeg" // register JPEG decoder for DecodeConfig
_ "image/png" // register PNG decoder for DecodeConfig
"io"
"log/slog"
"net/http"
"net/url"
"strconv"
"strings"
"time"
"gogobee/internal/safehttp"
_ "golang.org/x/image/webp" // register WebP decoder for DecodeConfig
"maunium.net/go/mautrix/event"
"maunium.net/go/mautrix/id"
)
// thumbnailUserAgent identifies the bot when probing and downloading the
// preview image for a posted link.
const thumbnailUserAgent = "GogoBee/1.0 (+link thumbnail fetch)"
// thumbnailClient validates and downloads link-supplied image URLs. It routes
// through safehttp so a posted link can't steer fetches at loopback / RFC1918 /
// cloud-metadata IPs — the dial-time guard re-checks every redirect target too.
// The 10 MiB download ceiling below bounds memory regardless.
var thumbnailClient = safehttp.NewClient(15 * time.Second)
// resolveURL turns a possibly-relative ref into an absolute URL against base.
func resolveURL(base, ref string) string {
ref = strings.TrimSpace(ref)
if ref == "" {
return ""
}
b, err := url.Parse(base)
if err != nil {
return ref
}
r, err := url.Parse(ref)
if err != nil {
return ref
}
return b.ResolveReference(r).String()
}
// normalizeImageURL rewrites known CDN thumbnail URLs to a higher-resolution
// variant. Currently handles The Guardian's i.guim.co.uk, whose pages hand out
// narrow thumbnails. Signed URLs are left alone (re-signing isn't possible),
// as are unrecognized hosts.
func normalizeImageURL(raw string) string {
if raw == "" {
return raw
}
u, err := url.Parse(raw)
if err != nil || u.Host != "i.guim.co.uk" {
return raw
}
q := u.Query()
if q.Get("width") == "" || q.Get("s") != "" {
return raw
}
q.Set("width", "1200")
u.RawQuery = q.Encode()
return u.String()
}
// validateImageURL HEAD-probes an image URL: it must be http(s), return 200,
// have an image/* content type, and (if a length is declared) exceed 5 KiB so
// tracking pixels are filtered. Returns false with no error on any failure.
func validateImageURL(rawURL string) bool {
if rawURL == "" || safehttp.ValidateURL(rawURL) != nil {
return false
}
req, err := http.NewRequest("HEAD", rawURL, nil)
if err != nil {
return false
}
req.Header.Set("User-Agent", thumbnailUserAgent)
resp, err := thumbnailClient.Do(req)
if err != nil {
slog.Debug("thumbnail: image HEAD failed", "url", rawURL, "err", err)
return false
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return false
}
if !strings.HasPrefix(resp.Header.Get("Content-Type"), "image/") {
return false
}
if cl := resp.Header.Get("Content-Length"); cl != "" {
if size, err := strconv.ParseInt(cl, 10, 64); err == nil && size <= 5120 {
return false // tracking pixel
}
}
return true
}
// SendImageFromURL downloads imageURL, uploads it to Matrix, and posts it as an
// m.image event in roomID. Returns an error on any failure so callers can fall
// back to a text-only preview. The fetch is SSRF-guarded and size-capped.
func (b *Base) SendImageFromURL(roomID id.RoomID, imageURL string) error {
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
req, err := http.NewRequestWithContext(ctx, "GET", imageURL, nil)
if err != nil {
return fmt.Errorf("create image request: %w", err)
}
req.Header.Set("User-Agent", thumbnailUserAgent)
resp, err := thumbnailClient.Do(req)
if err != nil {
return fmt.Errorf("download image: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return fmt.Errorf("image download status %d", resp.StatusCode)
}
data, err := io.ReadAll(io.LimitReader(resp.Body, 10*1024*1024))
if err != nil {
return fmt.Errorf("read image: %w", err)
}
contentType := resp.Header.Get("Content-Type")
if i := strings.IndexByte(contentType, ';'); i >= 0 {
contentType = strings.TrimSpace(contentType[:i])
}
if contentType == "" {
contentType = "image/jpeg"
}
if !strings.HasPrefix(contentType, "image/") {
return fmt.Errorf("not an image: %s", contentType)
}
// Decode dimensions so clients render the image inline rather than as a
// downloadable file attachment.
var width, height int
if cfg, _, decErr := image.DecodeConfig(bytes.NewReader(data)); decErr == nil {
width, height = cfg.Width, cfg.Height
}
ext := ".jpg"
switch contentType {
case "image/png":
ext = ".png"
case "image/gif":
ext = ".gif"
case "image/webp":
ext = ".webp"
}
filename := "thumbnail" + ext
uri, err := b.UploadContent(data, contentType, filename)
if err != nil {
return fmt.Errorf("upload image: %w", err)
}
content := &event.MessageEventContent{
MsgType: event.MsgImage,
Body: filename,
FileName: filename,
URL: uri.CUString(),
Info: &event.FileInfo{
MimeType: contentType,
Size: len(data),
Width: width,
Height: height,
},
}
_, err = b.Client.SendMessageEvent(context.Background(), roomID, event.EventMessage, content)
return err
}

View File

@@ -0,0 +1,40 @@
package plugin
import "testing"
func TestResolveURL(t *testing.T) {
cases := []struct {
base, ref, want string
}{
{"https://e.com/news/story", "https://cdn.e.com/a.jpg", "https://cdn.e.com/a.jpg"},
{"https://e.com/news/story", "//cdn.e.com/a.jpg", "https://cdn.e.com/a.jpg"},
{"https://e.com/news/story", "/img/a.jpg", "https://e.com/img/a.jpg"},
{"https://e.com/news/story", "a.jpg", "https://e.com/news/a.jpg"},
{"https://e.com/news/story", "", ""},
}
for _, c := range cases {
if got := resolveURL(c.base, c.ref); got != c.want {
t.Errorf("resolveURL(%q, %q) = %q, want %q", c.base, c.ref, got, c.want)
}
}
}
func TestNormalizeImageURL(t *testing.T) {
cases := []struct {
name, in, want string
}{
{"non-guardian passthrough", "https://e.com/a.jpg?width=140", "https://e.com/a.jpg?width=140"},
{"signed left alone", "https://i.guim.co.uk/x.jpg?width=140&s=abc", "https://i.guim.co.uk/x.jpg?width=140&s=abc"},
{"no width passthrough", "https://i.guim.co.uk/x.jpg", "https://i.guim.co.uk/x.jpg"},
{"empty", "", ""},
}
for _, c := range cases {
if got := normalizeImageURL(c.in); got != c.want {
t.Errorf("%s: normalizeImageURL(%q) = %q, want %q", c.name, c.in, got, c.want)
}
}
// Unsigned Guardian thumbnail gets bumped to width=1200.
if got := normalizeImageURL("https://i.guim.co.uk/x.jpg?width=140"); got != "https://i.guim.co.uk/x.jpg?width=1200" {
t.Errorf("normalizeImageURL unsigned = %q, want width=1200", got)
}
}

View File

@@ -10,6 +10,7 @@ import (
"time" "time"
"gogobee/internal/db" "gogobee/internal/db"
"gogobee/internal/safehttp"
"github.com/PuerkitoBio/goquery" "github.com/PuerkitoBio/goquery"
"maunium.net/go/mautrix" "maunium.net/go/mautrix"
@@ -40,9 +41,10 @@ func NewURLsPlugin(client *mautrix.Client) *URLsPlugin {
Base: NewBase(client), Base: NewBase(client),
enabled: enabled, enabled: enabled,
ignoreUsers: ignore, ignoreUsers: ignore,
httpClient: &http.Client{ // Route page scrapes through safehttp so a posted link can't steer the
Timeout: 3 * time.Second, // fetch at loopback / RFC1918 / cloud-metadata IPs (re-checked on every
}, // redirect), and can't OOM the parser by streaming an unbounded body.
httpClient: safehttp.NewClient(8 * time.Second),
} }
} }
@@ -90,12 +92,23 @@ func (p *URLsPlugin) OnMessage(ctx MessageContext) error {
} }
func (p *URLsPlugin) previewURL(ctx MessageContext, targetURL string) { func (p *URLsPlugin) previewURL(ctx MessageContext, targetURL string) {
title, desc, err := p.fetchPreview(targetURL) title, desc, image, err := p.fetchPreview(targetURL)
if err != nil { if err != nil {
slog.Debug("urls: fetch preview failed", "url", targetURL, "err", err) slog.Debug("urls: fetch preview failed", "url", targetURL, "err", err)
return return
} }
if title == "" && desc == "" && image == "" {
return
}
// Post the thumbnail first (best-effort), so it renders above the text.
if image != "" && validateImageURL(image) {
if err := p.SendImageFromURL(ctx.RoomID, image); err != nil {
slog.Debug("urls: thumbnail post failed", "url", targetURL, "image", image, "err", err)
}
}
if title == "" && desc == "" { if title == "" && desc == "" {
return return
} }
@@ -120,63 +133,69 @@ func (p *URLsPlugin) previewURL(ctx MessageContext, targetURL string) {
} }
} }
// fetchPreview retrieves og:title and og:description, checking cache first. // fetchPreview retrieves og:title, og:description and og:image, checking cache first.
func (p *URLsPlugin) fetchPreview(rawURL string) (string, string, error) { func (p *URLsPlugin) fetchPreview(rawURL string) (title, desc, image string, err error) {
d := db.Get() d := db.Get()
now := time.Now().UTC().Unix() now := time.Now().UTC().Unix()
cacheTTL := int64(24 * 60 * 60) cacheTTL := int64(24 * 60 * 60)
// Check cache // Check cache
var title, desc string
var cachedAt int64 var cachedAt int64
err := d.QueryRow( err = d.QueryRow(
`SELECT title, description, cached_at FROM url_cache WHERE url = ?`, rawURL, `SELECT title, description, image_url, cached_at FROM url_cache WHERE url = ?`, rawURL,
).Scan(&title, &desc, &cachedAt) ).Scan(&title, &desc, &image, &cachedAt)
if err == nil && now-cachedAt < cacheTTL { if err == nil && now-cachedAt < cacheTTL {
return title, desc, nil return title, desc, image, nil
} }
// Fetch from web // Fetch from web
title, desc, err = p.scrapeOG(rawURL) title, desc, image, err = p.scrapeOG(rawURL)
if err != nil { if err != nil {
return "", "", err return "", "", "", err
} }
// Cache the result // Cache the result
db.Exec("urls: cache write", db.Exec("urls: cache write",
`INSERT INTO url_cache (url, title, description, cached_at) VALUES (?, ?, ?, ?) `INSERT INTO url_cache (url, title, description, image_url, cached_at) VALUES (?, ?, ?, ?, ?)
ON CONFLICT(url) DO UPDATE SET title = ?, description = ?, cached_at = ?`, ON CONFLICT(url) DO UPDATE SET title = ?, description = ?, image_url = ?, cached_at = ?`,
rawURL, title, desc, now, title, desc, now, rawURL, title, desc, image, now, title, desc, image, now,
) )
return title, desc, nil return title, desc, image, nil
} }
// scrapeOG fetches a URL and extracts og:title and og:description. // scrapeOG fetches a URL and extracts og:title, og:description and og:image.
func (p *URLsPlugin) scrapeOG(rawURL string) (string, string, error) { func (p *URLsPlugin) scrapeOG(rawURL string) (string, string, string, error) {
if err := safehttp.ValidateURL(rawURL); err != nil {
return "", "", "", err
}
req, err := http.NewRequest("GET", rawURL, nil) req, err := http.NewRequest("GET", rawURL, nil)
if err != nil { if err != nil {
return "", "", fmt.Errorf("create request: %w", err) return "", "", "", fmt.Errorf("create request: %w", err)
} }
req.Header.Set("User-Agent", "GogoBee Bot/1.0") req.Header.Set("User-Agent", "GogoBee Bot/1.0")
req.Header.Set("Accept", "text/html,application/xhtml+xml")
resp, err := p.httpClient.Do(req) resp, err := p.httpClient.Do(req)
if err != nil { if err != nil {
return "", "", fmt.Errorf("fetch: %w", err) return "", "", "", fmt.Errorf("fetch: %w", err)
} }
defer resp.Body.Close() defer resp.Body.Close()
if resp.StatusCode != http.StatusOK { if resp.StatusCode != http.StatusOK {
return "", "", fmt.Errorf("status %d", resp.StatusCode) return "", "", "", fmt.Errorf("status %d", resp.StatusCode)
} }
doc, err := goquery.NewDocumentFromReader(resp.Body) // Cap the parsed body at 2 MiB — og: tags live in <head>, near the top.
doc, err := goquery.NewDocumentFromReader(safehttp.LimitedBody(resp.Body, 2*1024*1024))
if err != nil { if err != nil {
return "", "", fmt.Errorf("parse HTML: %w", err) return "", "", "", fmt.Errorf("parse HTML: %w", err)
} }
title := "" title := ""
desc := "" desc := ""
image := ""
doc.Find("meta").Each(func(_ int, s *goquery.Selection) { doc.Find("meta").Each(func(_ int, s *goquery.Selection) {
prop, _ := s.Attr("property") prop, _ := s.Attr("property")
@@ -186,6 +205,10 @@ func (p *URLsPlugin) scrapeOG(rawURL string) (string, string, error) {
title = content title = content
case "og:description": case "og:description":
desc = content desc = content
case "og:image:secure_url", "og:image:url", "og:image":
if image == "" && strings.TrimSpace(content) != "" {
image = content
}
} }
}) })
@@ -205,5 +228,9 @@ func (p *URLsPlugin) scrapeOG(rawURL string) (string, string, error) {
}) })
} }
return strings.TrimSpace(title), strings.TrimSpace(desc), nil if image != "" {
image = normalizeImageURL(resolveURL(rawURL, strings.TrimSpace(image)))
}
return strings.TrimSpace(title), strings.TrimSpace(desc), image, nil
} }

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@@ -0,0 +1,146 @@
// Package safehttp provides an http.Client hardened against SSRF and
// memory-DoS via hostile upstreams. Every outbound fetch the bot makes
// against feed-supplied URLs (RSS articles, image hosts) should go through
// one of these clients so a malicious feed can't steer the bot at loopback,
// link-local, RFC1918, or cloud metadata IPs, and can't OOM the process by
// streaming an unbounded body.
package safehttp
import (
"context"
"errors"
"fmt"
"io"
"net"
"net/http"
"net/url"
"strings"
"time"
)
// ErrBlockedHost is returned when a URL resolves to a non-public IP.
var ErrBlockedHost = errors.New("safehttp: blocked non-public host")
// AllowPrivate, when true, disables the loopback/RFC1918 dial guard. It
// exists for tests that spin up httptest.NewServer on 127.0.0.1 — never
// set this in production.
var AllowPrivate bool
// safeDialContext refuses connections to non-public IPs. It runs after
// DNS resolution, so a hostile DNS rebinding that returns 127.0.0.1
// still gets blocked at dial time.
func safeDialContext(ctx context.Context, network, addr string) (net.Conn, error) {
host, port, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
ips, err := (&net.Resolver{}).LookupIP(ctx, "ip", host)
if err != nil {
return nil, err
}
var allowed net.IP
for _, ip := range ips {
if AllowPrivate || isPublicIP(ip) {
allowed = ip
break
}
}
if allowed == nil {
return nil, fmt.Errorf("%w: %s", ErrBlockedHost, host)
}
d := &net.Dialer{Timeout: 5 * time.Second, KeepAlive: 30 * time.Second}
return d.DialContext(ctx, network, net.JoinHostPort(allowed.String(), port))
}
// isPublicIP reports whether ip is a globally routable unicast address.
// Rejects loopback, link-local, multicast, RFC1918, CGNAT, and the
// AWS/GCP/Azure metadata IPs 169.254.169.254 / fd00:ec2::254 (these
// already fall under link-local but spell it out for clarity).
func isPublicIP(ip net.IP) bool {
if ip == nil || ip.IsUnspecified() || ip.IsLoopback() ||
ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() ||
ip.IsMulticast() || ip.IsPrivate() {
return false
}
// 100.64.0.0/10 (CGNAT) is not covered by IsPrivate on older Go.
if v4 := ip.To4(); v4 != nil {
if v4[0] == 100 && v4[1] >= 64 && v4[1] <= 127 {
return false
}
// 0.0.0.0/8 and friends.
if v4[0] == 0 {
return false
}
}
return true
}
// ValidateURL returns nil if the URL is http(s) and parseable. It does
// not resolve DNS — the dial step does that — but it does reject bare
// schemes (file://, gopher://, etc.) before we even open a connection.
func ValidateURL(raw string) error {
u, err := url.Parse(strings.TrimSpace(raw))
if err != nil {
return err
}
if u.Scheme != "http" && u.Scheme != "https" {
return fmt.Errorf("safehttp: unsupported scheme %q", u.Scheme)
}
if u.Host == "" {
return errors.New("safehttp: empty host")
}
return nil
}
// NewClient returns an http.Client whose transport blocks non-public
// destinations at dial time, caps redirects at 5, and re-validates each
// redirect target's scheme. timeout is the per-request overall budget.
func NewClient(timeout time.Duration) *http.Client {
tr := &http.Transport{
DialContext: safeDialContext,
ForceAttemptHTTP2: true,
MaxIdleConns: 32,
IdleConnTimeout: 90 * time.Second,
TLSHandshakeTimeout: 5 * time.Second,
ExpectContinueTimeout: 1 * time.Second,
ResponseHeaderTimeout: 10 * time.Second,
}
return &http.Client{
Transport: tr,
Timeout: timeout,
CheckRedirect: func(req *http.Request, via []*http.Request) error {
if len(via) >= 5 {
return errors.New("safehttp: stopped after 5 redirects")
}
if req.URL.Scheme != "http" && req.URL.Scheme != "https" {
return fmt.Errorf("safehttp: unsupported redirect scheme %q", req.URL.Scheme)
}
return nil
},
}
}
// LimitedBody wraps r in a reader that errors once more than max bytes have
// been read. Use to cap how much of a response body downstream parsers
// (goquery, image.Decode) will ever see — a hostile origin streaming an
// endless body otherwise OOMs the process.
func LimitedBody(r io.Reader, max int64) io.Reader {
return &limitedReader{R: r, N: max}
}
type limitedReader struct {
R io.Reader
N int64
}
func (l *limitedReader) Read(p []byte) (int, error) {
if l.N <= 0 {
return 0, fmt.Errorf("safehttp: response body exceeded cap")
}
if int64(len(p)) > l.N {
p = p[:l.N]
}
n, err := l.R.Read(p)
l.N -= int64(n)
return n, err
}

View File

@@ -406,8 +406,8 @@ func setupScheduledJobs(
} }
}) })
// WOTD post at 08:00 // WOTD post at 08:00 (disabled by default; opt in via ENABLE_WOTD_POST=true)
if strings.ToLower(os.Getenv("DISABLE_WOTD_POST")) != "true" { if strings.ToLower(os.Getenv("ENABLE_WOTD_POST")) == "true" {
c.AddFunc("0 8 * * *", func() { c.AddFunc("0 8 * * *", func() {
slog.Info("scheduler: posting WOTD") slog.Info("scheduler: posting WOTD")
for _, r := range rooms { for _, r := range rooms {
@@ -415,7 +415,7 @@ func setupScheduledJobs(
} }
}) })
} else { } else {
slog.Info("scheduler: WOTD daily post disabled via DISABLE_WOTD_POST") slog.Info("scheduler: WOTD daily post disabled (set ENABLE_WOTD_POST=true to enable)")
} }
// Game releases Monday 09:00 // Game releases Monday 09:00